2- Go to local hardware or home imp. store: they have people who can tell you what you need and how to do it
3- Go to thisoldhouse.com -how to videos and watch some of the window videos. These are very helpful, especially concerning sash windows.
tools: regular hand tools, maybe a power drill with screwdriver bits, a good utility knife, putty knife. goggles, gloves, caulk, insulation, and wood shims. Plus - nails
I replaced some of these a few years ago - slow at first, but after the first two, it was easy.
Go to a home improvement store [like Lowe's, Home Depot, etc.], or almost any bookstore, and get one of those paperback Do-It-Yourself booklets on basics of home improvement as they usually contain info on this subject.
Also, VERY IMPORTANT, as a previous answer said, "Follow the instructions" that come with the new windows. I also recommend that you read and study those instructions a half dozen or so times, or until you FULLY understand them, BEFORE you even try to start the job.
One of the biggest mistakes made by home imrovement novices is to try to do a job for which they are unprepared.